A skin is provided as a boundary between a living body and an external environment and has functions of maintaining a liquid in the living body, reducing friction in water, keeping body temperature constant, and protecting the inside of the living body from physical damages.
The skin of a vertebrate animal consists of a connective tissue layer generally regarded as dermis originated from the mesoderm and epidermis stratified thereon originated from the ectoderm.
Cultured skin is constructed from a part of a skin structure by in vitro culture of epithelium cells (i.e., epithelial cells) and fibroblasts collected from a piece of healthy skin (a piece of epithelium). It is also referred to as autologous cultured skin when cells collected from a piece of a patient's own healthy skin (a piece of epithelium) are used or an allogeneic cultured skin when cells collected from a piece of healthy skin (a piece of epithelium) of another patient are used.
The cultured skins can be applied in medical treatments for severe burns, diabetic ulcers of lower limbs, and venous ulcerative inflammation, treatment of scars after plastic surgery, and so on. The cultured skins are not only effective in simply covering a wounded surface but are also effective in secreting or supplying growth factors or the like required for wound healing.
Currently, as sources for supplying human functional epithelium cells, cultured skins using constructive materials prepared from neonatal and adult penis foreskins, epithelium cells originated from oral mucosa, fibroblasts originated from skins, and matrices including collagen, fibrin, heparin, silicon, and so on have been reported (JP-A 246371/1987, JP-A 332561/1992, JP-A 125855/2000, JP-A 157624/2000, Japanese Patent No. 3105308, and “Nikkei Bio Nenkan 2000”)
However, epithelium cells of the tissues provided as origins of the above cells are those in which cell differentiation and aging have progressed, so that their cell division lifetime may be short and their capacity for differential plasticity may be small. Furthermore, there are many unsolved problems in the art. For instance, there are variations in the collections of cell populations, instability of healthy tissues, dimensions of tissues, and so on. Ethical problems are caused in offering of an excess normal tissue obtained at the time of surgical operations, and so on.